1. Field of the Invention
The present invention relates to data communications, and more particularly to techniques for improving the flexibility and useability of point-to-point communication protocols, such as the Point-to-Point Protocol (PPP), for static link modems, such as Asynchronous Digital Subscriber Loop ADSL modems.
2. Description of Related Art
The Point-to-Point Protocol, as it is defined, is used for transporting multi-protocol datagrams over point-to-point links. One version of the PPP is described in Request For Comments RFC 1661, published July 1994 by the Point-to-Point Protocol Working Group of the Internet Engineering Task Force IETF. The PPP consists of a specification for encapsulating multi-protocol datagrams, a link control protocol LCP for establishing, configuring and testing the datalink connection, and a family of network control protocols NCPs for establishing and configuring different network layer protocols. According to the PPP, network layer packets are referred to as datagrams. The datagrams are passed to the datalink layer in which they are encapsulated according to the PPP in a packet having a packet header. The packet including the PPP fields and the datagram is passed to the physical layer at which framing such as HDLC-like framing is appended to form a frame in the format received at the physical layer interface. So called HDLC-like framing is described in "PPP in HDLC-like Framing" RFC 1662 published July 1994 by the Point-to-Point Protocol Working Group of the IETF. Upon reception, the frame is stripped of its framing fields, and a packet is passed to the datalink layer. The packet is stripped of its control fields to produce a datagram. The datagram is passed to the network layer at which network layer headers and the like are processed. Use of the PPP provides a simple technique for encapsulating data from a variety of protocols and is used for example across telephone lines between end stations and Internet access providers.
PPP sessions are established between peers. In one typical environment, the peers include equipment located at a customer site referred to as customer premises equipment CPE, and a remote access server RAS operated by an Internet Service Provider ISP. The customer typically dials a telephone number to access the RAS of the Internet Service Provider. For some modem types, such as the asynchronous digital subscriber loop ADSL (running PPP in HDLC framing over ADSL), the CPE has a static link to a RAS, without requiring dial up. In this case the central office switch is statically configured to direct ADSL traffic from a particular modem to a particular destination, such as a remote access server for an Internet Service Provider. The PPP is utilized to establish the peer to peer connection from the CPE to the RAS.
Thus, when a CPE is connected via ADSL to a central office switch and uses a protocol, such as the PPP over HDLC-like framing, without out-of-band session establishment, the user is limited to a single peer connection. Alternatively more, complex protocols, such as PPP over ATM on an ADSL link, provide a capability to set up more than one connection through the ATM procedures. However, it is desirable to provide this capability on simpler protocols.